Interrelated process of and apparatus for producing sulphate and sulphite pulp



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G. A. RCHTER INTERRELATED PROCESS OF AND APPARATUS FOR PRODUCING SULPHATE AND SULPHITE PULP Filed Aug. 18 1925 lu u rameau nee re, rear,

narran saar .atteste Nr time,

PAT

GEORGE A. RECHTER, 0F BERLN, NEW HAMPSHIRE, ASSIGNOR 'E0 BROWN CMPANY, 0F BERLN, NEW HAMPSHIRE, A CORPORATION 0F MAINE.

rn'rnna'rnn ronss or AND armenews For, Pacino-crue sonren .aun surirjnrrn anar.

application led Augustl, 1923. Serial No. 658,101.

To all whom it may concem:

Be it known that l, GEORGE A. RIoHTnR,'a citizen of the United States, residing at Berlin, in the county of Coos and State of New Hampshire,`have invented new and useful Improvements in linterrelatedProcesses of and Apparatus for Producing Sulphate and Sulphite Pulp, of which the vfollowing-is a specification.

ln Letters Patent No. 1,427,125, granted on August 29, 1922, l have described aprocess of producing sulphite pulp by digesting wood chips or other cellulosic material in the presence of an acidliquor consisting of a solution of sodium sulphate and sulphurous acid, and l have also explained that the soda may be recovered and again used. Although the acid solution which is employed therein for digesting the chips has as its base al solublesulphate, the pulp Vproduced may be referred to as sulphite pulp, in asmuch as the fiber liberation occurs in the presence of sulphurous acid.

rl`he object ofthe present invention is to provide for the simultaneous production of both sulphite and sulphate pulps with a marked economy of operation; to reduce the number of kinds of raw materials which are required for the production of these pulpe,

to reduce the quantity of lime which is ordinarily utilized for. causticization in a sulphate process of digestion to only that amount which is required because of relative differences inthe 4amount of the two pulps which are-produced simultaneously; and to prevent or reducer the accumulation of lime sludge which marks the ordinary commercial production of sulphate pulp.

In carrying out my invention, it is necessary to utilize as raw material only sulphur and caustic soda, the sulphur being utilized for producing SO, gas for the acidulation of the cooking liquor in the sulphite side of the system and for making up sulphur losses, and the caustic soda being added to the sulphate side of the system to make up losses of active alkali in the digestion of the pulp and in the recovery of the soda constituents in the smelting furnaces. A part of the sulphur may be also added in the sulphate side of the system to increase the sulphidity of the cooking liquor when required, as set Aforth in the application, Serial No. 421,769,

filed November 4, 1920'and renewed February 9, 1923, vfiled by' Douglas H. McMurtrie and myself. Theoretically, if the relative pulp productions are in correct proportion, thereis no necessity to use linie as a raw material, but inasmuch as in'practice it is practically impossible lto maintain the relative productions ofthe two forms of pulp in proper proportion, it is necessary tov employ certain amounts oflime for causticizing the raw liquor for use in the sulphate side of the system. l wish at this point to make it carrying` out my` interrelated process in which 'part of 'the wood chips are digested 'in' an alkaline liquor and the other part of the chips in an acid liquor, the waste liquor fromv each digester after being concentrated by the evaporation vof a part of'its aqueous constituent is delivered to a smelting lfurnace for the recovery of the inorganic content. rlhesetwo furnaces are preferably so arranged that Ain one there is maintainedH an oxidizing atmosphere for the recovery of a part of the soda in the form of sodium carbonate and sodium sulphate, while in the other furnace a reducing 4atmosphere is maintained for the recovery of the sodain the form of sodium sulphide and sodium carbonate with doubtless some sodium sulphate. The recovered smelt from the firstmentioned furnace is then acidiied for use as liquor in the sulphite digester, whereasy lthe smelt from the reducing smelting furnace, after being causticized if necessary, isv employed as the alkaline liquor in the sulphate digester. Thus it will be seen that the soda in one form or another passes in a cycle throu h the sulphate digester and through the su phite digester and back again. If in the recovery of the soda from the waste liquor of the sulphate digester it is exposed to a reducing atmosphere for the producltion of the alkali as sodium sulphide and sodium carbonate, that whichk is recovered maybe used in forming fresh liquor for the same sulphate digester, in which case a part of the waste liquor is diverted before it reaches the sinelting furnace and is delivered for admixture with and the neutralization of the waste acid liquor from the sul# phite digester, so that its mineral constituents are then/recovered .together with the.

mineral constituents of the sulphite waste liquor` in the form of sodium carbonate and sodium sulphate, inasmuch as in the smelting furnace last-mentioned an oxidizing atmosphere has been maintainedq-so'that in either case whether the recovery of the min-` eral constituents of the sulphite waste liquor is accomplished in the presence of an oxidizing or a reducing'atmosphere, and the mineral contents of the waste liquor from the sulphite digester 1s accomplished in the presence of an oxidizing or a reducing atmosphere, a part of the sulphur and the soda is caused to traverse in one form or another throughout the entire system and be utilized in the formation of lboth the. acid and the alkaline cooking liquors..

On the accompanying drawing I have shown diagrammatically and most conven-n tionally a system for pulp liberation, said system including the various instrumentalities which may be employed in carrying out the` interrelated processes embodying my 1nvention. using the term system, I mean thereby to include the various me-I chanical instrumentalitiesl and connections -which constitute a means for the practice of the entire process. l

Referring to drawings, 1 indicates what may be termed for convenience the sulphate y digester of the system, inasmuch as thepulp the usual length of time, the contents of the digester are delivered through a. pipe or conduit 2 to a blow-pit or receptacle 3. Through ascreened'outlet indicated at 4 a part of the black liquor may be forced by a pump through a pipe 6 to a tank 7, whichv for convenience may be termed a tank for undiluted black liquor. From this tank a certain amount df the black liquor-may be delivered by a valved pipe 8 to the top of the digester phate or sulphide.

for the next cook, inasmuch as the liquor contains a certain small quantity of sodium sulphide and caustic soda. From the blowpit 3 the pulp and the remainder of the black liquor may be forced by a pump 9 through a conduit 10 to any suitable washing machine, by which the pulp is washed and separated from the black liquor. I preferably employ for this purpose a washing machine such as illustrated and described in Letters Patent, No. 1,421,664, dated July 4, 1922, to BrownMartinson, Moore and Parker- The pulp which is separated during the washing process is transmitted by a conduit 11 to theusual screens (not shown) wherein knots,- specks and foreign matter are removed from the pulp so that the latter may be employed. for the manufacture of paper. On the drawing, the Washing machine is only conventionally illustrated and is indicated at 12. Subsequently I will explain the treatment vto which thev black liquor is subjected after delivery from the washing machine 12. l At 13 I have indicated a-digestcr for the digestion of cellulosic material in an acid cooking liquor, and to distinguish it, this digester is here referred to as the sulphite digester, inasmuch as the cooking liquor is acid. In-this case the cooking liquor consists of an acidv solution of al soluble sulphate and preferably a soluble sulphite such as disclosed in my application, lSerial No. 661,24() filed September 6, 1923. Preferably this acid liquor comprises about .4% to 7 free -SO2 and 0.2% to 2% combined SO2 as sodium4 sulphite and 2% to 4% sodium sulphate. In this case it will be noted that the basic metal employed in the 'formation of the cooking liquor in both digesters is the same, namely sodium, and that sulphur is employed'in both liquors, either as SO2, or in combination with sodium'as sulphite, sul- The sodium is combined as caustic soda and sodium sulphide in the alkaline liquor and is combined as sodium sulphate and sodium sulphite in the acid liquor. vAfter the chips have been cooked at a temperature of say 275o to 300 F. for ten to twelve hours in the digester 13, the contents of the digester are blown through the blowpipe 14 to a blow-pit indicated at 16. From this blow-pit the waste liquor and the pulp are forced by a pump 17 through a condult 18 to a storage tank .19, from which they are pumped by a pump 20 through a conduit 21 to a pulp washing machine indicated as a whole at 22. This washing machine is preferably substantially similar to that 'indicated conventionally at 12. After the separation of the pulp from the waste 'liquor, it is conducted through a conduit 23 to the usual screens (not shown) prior tthe formation of the screened pulp into paper. The pulp produced by the cooking operaloe yet

heiratet tion in digester No. 1 is herein termed sulhate pulp, while that produced from the digested 13 -is designated sulphite pulp, partly because of the commercial usage of the former term and in order to distinguish the pulp produced in the digester 13 from that pulp commercially known as sulphate ul p 'llphere remains now to be described the means by which the soda is recovered from the waste liquor on the two sides of lthe system and utilized in both processes of digestion. ln each case the waste liquor is concentrated by the evaporation of a portion of its water content in any convenient manner and the residuum is smelted in a smelting furnace for the recovery of the soda in one or another of several compounds. Preferably `for the concentration of the waste liquor 'in each case l employ a multiple-effect evaporator, that for the alkaline waste liquor being indicated conventionally at 24 and that for Vthe acid liquor being indicated at 25. n

the drawing it will be observed that there is a conduit 26 f deliveringthe alkaline waste liquor to the multiple-edect evaporator '24 and aV conduit 27 for delivering the acid liquor from the washing machine to the .multiple-elfect evaporator 25. 28 cate two smelting furnaces. Preferably -ll employ that type of combined smelting and boiler furnace which is illustrated and described in the patent to Moore and Quinn, No. 1,326,414, dated December 30, 1919, in which case the waste liquor is first heated while maintained under external pressure so as to generate therein an explosive force so that when liberated in the combustion chamber of the furnace the waste liquor is disintegrated and the combustible content thereof consumed, and although on the drawings the furnaces are only conventionally indicated, one may, by referring to the Letters Patent last herein referred to, obtain the details of the furnaces .which l prefer tov employ. There is this dierence, however, between the two furnaces which l utilize; namely, thatV in one case the smelt is subjected to a reducing atmosphere, whereas in the other, the smelt is subjected to an oxidizing atmosphere. ln the present instance the furnace in which a reducing atmosphere is maintained is that *indicated at 29, in order that a portion of the soda may be recovered in the form of sodium sulphide as well as sodium carbonate, together'with some sodium sulphate. rlhe furnace 28, n the other hand, in the present instance is the one in which an oxidizing atmosphere is maintained so that the f soda is recovered.

from lthe alkaline liquor in the form of sodium carbonate and sodium sulphate. The acid liquor should be neutralizedl preferably before it' is evaporated and burned, and consequently from thel dissolving tank 30 and 29 indiinto which a part-of the smelt from the furgester. A sufiicient quantity of this alkaline liquor is mixed with the acid liquor in the storage tank 19 to neutralize it.

rlhe smeltfrom the reducing smelting furnace 29 is delivered into a dissolving tank 33 containing water so that the sodium compounds-which are soluble may be dissolved therein. This' solution comprising sodium sulphide, sodium carbonate and some sodium sulphate ordinarily requires to be causticized by the addition of lime and consequently l have illustrated on the drawing at 34 a causticizing tank equipped with an agitator. A sucient quantity of lime is added for reaction with the sodium cdrbonate for the production of caustic soda. After the caustipizing operation, the liquor is pumped by a pump 35 through a conduit 36. and a filter press 37 to a mixing tank 38, so that there may now be added toV the alkaline liquor sucient caustic soda to make up losses occurring in the original liquor during the digestion and the recovery of the soda. lhave indicated conventionally at 39 a tank for containing a caustic soda solution, a portion of the contents of which may be delivered through a valve pipe 4() to the mixing tank 38. From this mixing tank thealkaline liq uor may now be pumped by a pump 41 through a pipe 42 to the sulphate digester 1 for the cooking of a fresh batch of chips. Any deiciency in sulphidity may be made up by adding sulphur to the mixing tank from a receptacle 43. Sulphur in any event is added, on the. sulphite side of the system, in the form of St), from the sulphur-burner gases, in acidifying the cooking liquor for digester 13.

Returning now to the recoilered soda from the oxidizing furnace 28, the greater part ofl the smelt is delivered to a dissolving tank 44 containing water or an alkaline liquor.

This solution which, it will be recalled, contains both sulphate and carbonate of soda is nowiready to be acidulated for use in digester 13 for the production of sulphite pulp. Any suitable apparatus may beutilized for acidulating this liquor, so that ll have indicated conventionally at 45 a pair of towers through which the alkaline solution'may be passed in series and in counter-current flow to S02 gas for supplying the solution with suficient sulphur dioxide 'to/ convert the sodium carbonate to sodium sulphate and sodium sulphite and to furnish the solution with the requisite amount of freeSOg. \@n the drawing, l have indicated a pump 46 by which the alkaline liquor from the dissolving tank 44`is pumped through a pipe 47 to the top of the left-hand tower indicated at 45. Each of these towers is preferably provided with a mass of inert interstitial material such as spiral brick. The liquor after passing through the left-hand tower is pumped by pump 48 through pipe 49 to the top of the right-hand tower, and after emerging from the bottom of the last-mentioned tower is delivered byV a conduit 50 to a storage tankml, from-which it may be "forced by a pump 52 through pipe 53 to the top of the digester 13 for use in cooking a batch of. chips therein. Sulphur burner gas may be delivered to the lower end of the righthand tower through a gas main 54, and after passing upwardly through the tower is conducted by a conduit 55 to the lower end of the left-hand tower from the top of which the waste gases arel vented through an outlet 56. I may reiterate that in describing the conventionally illustrated towers for acidulating) the alkaline liquor so that it may be used in the sulphite digester there is no intention on my part to indicate that -other forms of 'apparatus may not be used, as ordinarily I employ acid gas such as relieved from the sulphite digester in effecting a high acidulation of the-liquor.

From the foregoing description, it will be apparent that vthe soda which is dissolved in the acid liqluor employed in the product1on of the su phite pulp is recovered and -utilized in an alkaline liquor for -the production of sulphate pulp and, conversely, the soda in the waste alkaline liquor fro-m the sulphate digester is recovered and employed in an acid liquor for the production of sulphite pulp., Consequently,the soda in a soluble form is carriedin a complete cycle through thesulphate and sulphite digesters for -t-he digestion of the raw cellulosic ma.

terials.

There are lmany other advantages incident to the process which I have herein described and which will be apparent to those skilled in the art without my attemptingtoenumerate them. I may advert to the fact,`how

ever, that there is decided advantage in employing as raw materials only caustic soda and sulphur, both of which, as previously stated, may be introduced in the sulphate side of. the system herein described. It is true that in practical operation due to the impossibility of maintaining a relative' pulp production on both sides of the system, a

certain quantity of lime must also be em-- ployed for causticizing the soda ash priorto its/delivery to the sulphate side of the system,'but it is quite apparent that the amount of lime which thus must be employed is much less than that which isordinarily employed in the usual sulphate process of pulp production. At the risk of repetition, I may call attention to the fact that in the production of sulphite cooking acid liquor for vthe system is as suitable vfor reaction with.

SO2 to form sodium sulphite 4as caustic soda would be, whereas the caustic soda supplied to the liquor for the sulphate digestion're-v places Athat sodium carbonatewhich is ordinarily used and which vrequires lime for causticization. The amount yof lime saved corresponds `to theamount of sodium carbonate delivered from'- the sulphate side of the system, this amount of sodium carbonate being equivalent to sodium losses in the sulphite side of the System. For example, if in the sulphite side of the system there is soda ash per lton of pulp, this is replacedv by an equivalent amount of4 sodium carbonate from the sulphate side of the system,

which in turn is compensated for by a so- \dium constituent in the 'form of sodium hydroxide, directly supplied to the alkaline cooking liquor so that there is a resulting saving of lime. A

0n the drawing, which is wholly conventional and diagrammatic, I have made no attempt to indicate the relative dimensions andlocation' of the various instrumentalities or tol show the details of the several instrumentalities. For example, I have omitted, as'being no part of the present invention, any means for recovering and' using the relief from the sulphite digester,

atmosphere, and in which the soda content of the waste ,alkalinevliquor from the sulphate digester is recoveredin a reducing` atmosphere. Nor do I herein claim the sub- 'ject matter claimed in my said application Serial- No. 661,240. ,l

What I claim is 1. A process .of 'fiber liberation, whichcomprises digesting raw cellulosic material 1n an acld cooklng liquor containin a sollble soglium compound, digesting raw y cellulosic--material in an alkaline cooking liquorcontaining a soluble sodium compound, and recovering sodium compounds from the waste acid cooking liquor resulting from one digestion and using the same in the formation of the alkaline cooking liquor for lthe other digestion.

80 lost the equivalent of a certain amount of neraeoe 2. A process ot fiber liberation, which comprises digesting raw cellulosic material in an acid cooking liquor containing a soluble sodium compound, digesting raw cellulosic material in an alkaline cooking liquor containing a soluble sodium compound, and recovering sodium compounds from the waste cooking liquor resulting from one digestion and using the same in the formation of the cooking liquor for the other digestion, and vice versa.

3. A process of' liber liberation, which comprises cooking raw cellulosic materials, one batch in an acid liquor and another batch in an alkaline liquor, and using as the basic compound for the liquor of each batch, those soluble inorganic compounds recovered from the other liquor after the raw material is cooked therewith. l

4. A process of fiber liberation, which comprises cooking raw cellulosic material in two batches, one in an acid liquor containing sodium compounds and the other in an alkaline liquor containing sodium compounds, and forming each cooking liquor with sodium compounds recovered from the other liquor after the cooking therewith has been completed. i l

5. A process ofv fiber liberation, which comprises recovering sodium compounds from waste alkaline cooking liquor, forming an acid cooking liquor from such com-` pounds and cooking cellulosic material therewith, recovering sodium compounds from the acid waste liquor resulting therefrom, and forming an alkaline cooking liquor from such recovered sodium compounds.

6. A process of ber liberation, which comprises digesting raw cellulosic materials in successive batches, one in an alkaline cook'- ing liquor and the other in an acid cooking liquor, and forming each liquor with inorganic compounds derived and recovered from the other liquor after the cooking operation therewith.

7. .An interrelated process ot producing both sulphate and sulphite pulps from raw cellulosic materials, which comprises using compounds of the same basic metal successively in an alkaline cooking liquor and in an acid cooking liquor, by recovering compounds of said metal from each of such liquors, when spent, and employing such compounds in the formation of the other cooking liquor, and digesting hatches of raw cellulosic' materials with such acid and alkaline liquors respectively.

8. An interrelated process ot manufacturing sulphate and sulphite pulps Jtrom raw cellulosic materials, which comprises using compounds of the identical basic -y metal recovered from' lthe waste cooking producing one of such the cooking liquor for votr such pulps.

liquor employed in pulps in forming producing the other 9. An interrelated process oit manufacturing sulphate and sulphite pulps trom such liquors.

l0. vln the manufacture of chemical wood pulp, recovering sodium compounds from the alkaline waste liquor used in producing such pulp, forming a solution thereof, aciditying suchl solution with sulphur dioxide, and cooking cellulosic material with such acid solution.

l1. ,ln the manufacture of chemical wood pulp, 'cooking cellulosic material in a sulphurous acid solution of a sodium salt, cooking cellulosic material in an alkaline solution of another sodium compound, neutralizing the waste acid `cooking liquor with the waste alkaline cooking liquor, recovering sodium compounds from the resulting liquor in an alkaline solution, andlcooking cel-v lulosic material therewith.

1 2. ln the manufacture of chemical wood pulp, a cyclic process comprising cooking cellulosic material with an acid solution of sodium-sulphur compounds recovered from the waste hereinafter-mentioned alkaline cooking liquor, and cooking cellulosic material with an alkaline solution of sodiumsulphur compounds recovered from the waste first mentioned acid cooking liquor. 13. lin the manufacture of chemical wood pulp, a cyclic process comprising cooking cellulosic material with an acid solution of sodium-sulphur compounds recovered from the waste hereinafter-mentioned alkaline cooking liquor,l cooking cellulosic material. with anralkalinesolution of sodium-sulphui` compounds recovered from the waste said acid cooking liquor, and making up losses in sodium during such cyclic operation by adding soluble sodium compounds y to the alkaline'cooking liquor.

14. A process as herein described, comprising cooking raw cellulosic material in a sulphurous acid solution of sodium sulphate and sodium sulphiteneutralizing the waste acid cooking liquor,gsmelting the sodium compounds of said waste liquor in a reducing atmosphere and recovering the resulting sodium compounds .in an alkalinev solution, causticizing the said solution with lime and removing the resulting insoluble carbonate therefrom, and cooking cellulosic material in the nal alkaline solution,

l5. A process as herein described, comprising cooking raw cellulosic material in 'an alkaline solution of caustic soda and sodium sulphide, smelting the sodium comthe resulting sodium compounds in solution, .acdifying such solution With sulphur dipounds of the vWaste cooking liquor in'an 4oxidizing atmosphere and recovering the resulting sodium compounds in1 solution,

-acidifying such solutionwith .sulphur dil oxide, and cooking cellulosic material in' such acid solution. i 4

16. A process as her-ein described, comprising cooking raw ce'llulosic materialin an alkalfne solution ofcaustic soda and sodium sulphide, smelting the sodium compounds of the Waste cooking alkaline liquor in an oxidizing atmosphere and recovering oxide, cooking cellulosic material in such acid solution', smelting the sodium com` pounds of the waste acid cooking liquor and recovering the resulting sodium compounds in an alkalfne solution, causticizing any sodium carbonate in said solution with' lime and removing the Iresulting insoluble carbonate, and cooking raw cellulosic material in the resulting solution, thereby completing a c clic operation. l

17. processI as vherein described, comprising cookino raw cellulosic material in an alkaline soxlution of caustic soda and sodium sulphide, smelting the sodium compounds of the Waste alkaline cooking liquor in an oxidizing atmosphere, and recovering the resultin sodium compounds in solution, acidifymg such solution with sulphur dioxide, cooking cellulosic material in'such acid solution, smelting the sodium compounds of the waste' acid cooking liquor and recovering the resultingA sodium compounds 1n ,an alkaline lsolutlon, causticlzmg any sodium carbonatelin said solution withlime and removing the resulting insoluble carbonate, adding'caustic soda to' saidalkallne-solution.. to make up losses in sodium occasioned by the said operations, and cook- 1 ing cellulosic material.' with the resulting liquor, thereby completing a cyclic operation.

18. A processgas herein described, compri'sing cooking raw .cellulosic material in an alkaline solution of caustic soda and sodium sulphide, smelting the sodium compounds of the waste alkaline cooking liquorin an oxidizing vatmosphere and recovering the resulting sodium compounds in solution, acidifyng such solution with sulphur dioxide, cooking cellulosic material in such acid solution, smelting the sodium compounds of the Waste acid cooking liquor and recovering the resulting sodium compounds In testimony whereof I have aiiixed my signature.

f GEORGE A; RICHTER. 

